A semantic file system is an information storage system that provides flexible associative access to the system's contents by automatically extracting attributes from files with file type specific transducers. Associative access is provided by a conservative extension to existing tree-structured file system protocols, and by protocols that are designed specifically for content based access. Compatibility with existing file system protocols is provided by introducing the concept of a virtual directory. Virtual directory names are interpreted as queries, and thus provide flexible associative access to files and directories in a manner compatible with existing software. Rapid attribute-based access to file system contents is implemented by automatic extraction and indexing of key properties of file system objects. The automatic indexing of files and directories is called "semantic" because user programmable transducers use information about the semantics of updated file system objects to extract the properties for indexing. Experimental results from a semantic file system implementation support the thesis that semantic file systems present a more effective storage abstraction than do traditional tree structured file systems for information sharing and command level programming.

The purpose of a distributed file system (DFS) is to allow users of physically distributed computers to share data and storage resources by using a common file system. A typical configuration for a DFS is a collection of workstations and mainframes connected by a local area network (LAN). A DFS is implemented as part of the operating system of each of the connected computers. This paper establishes a viewpoint that emphasizes the dispersed structure and decentralization of both data and control in the design of such systems. It defines the concepts of transparency, fault tolerance, and scalability and discusses them in the context of DFSs. The paper claims that the principle of distributed operation is fundamental for a fault tolerant and scalable DFS design. It also presents alternatives for the semantics of sharing and methods for providing access to remote files. A survey of contemporary UNIX@-based systems, namely, UNIX United, Locus, Sprite, Sun’s Network File System, and ITC’s Andrew, illustrates the concepts and demonstrates various implementations and design alternatives. Based on the assessment of these systems, the paper makes the point that a departure from the approach of extending centralized file systems over a communication network is necessary to accomplish sound distributed file system design.

developed at the IBM Almaden Research Center, which uses atomic tran.sactions as a unified failure recovery mechanism for a client-server structured distributed system. Transactions allow failure atomicity for related activities at a single server or at a number of independent servers. Rather than bundling transaction management into a dedicated language or recoverable object manager, Quicksilver exposes the basic commit protocol and log recovery primi-tives, allowing clients and servers to tailor their recovery techniques to their specific needs. Servers can implement their own log recovery protocols rather than being required to use a system-defined protocol. These decisions allow servers to make their own choices to balance simplicity, efficiency, and recoverability. Categories and Subject Descriptors: D.4.3 [Operating Systems]: File System Management-distrib-uted file systems; file organization; maintenance; D.4.5 [Operating Systems]: Reliability-FauZt-tolerance; checkpoint/restart; H.2.4 [Database Management]: Systems--distributed systems; trun.s-action processing

This paper describes a workstation file system that supports a group of cooperating programmers by allowing them both to manage local naming environments and to share consistent versions of collections of software. The file system has access to the workstation's local disk and to remote file servers, and provides a hierarchical name space that includes the files on both. Local names can refer to local files or be attached to remote files. Remote files, which also may be referred to directly, are immutable and cached on the local disk. The file system is part of the Cedar experimental programming environment at Xerox PARC and has been in use since late 1983.

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This paper presents the design and implementation of a new authentication and access control system, called CRISIS. A goal of CRISIS is to explore the systematic application of a number of design principles to building highly secure systems, including: redundancy to eliminate single points of attack, caching to improve performance and availability over slow and unreliable wide area networks, fine-grained capabilities and roles to enable lightweight control of privilege, and complete local logging of all evidence used to make each access control decision. Measurements of a prototype CRISIS-enabled wide area file system show that in the common case CRISIS adds only marginal overhead relative to unprotected wide area accesses. 1 Introduction One of the promises of the Internet is to enable a new class of distributed applications that benefit from a seamless interface to global data and computational resources. A major obstacle to enabling such applications is the lack of a general, cohere...

v Abstract Caching has long been recognized as a powerful performance enhancement technique in many areas of computer design. Most modern computer systems include a hardware cache between the processor and main memory, and many operating systems include a software cache between the file system routines and the disk hardware. In a distributed file system, where the file systems of several client machines are separated from the server backing store by a communications network, it is desirable to have a cache of recently used file blocks at the client, to avoid some of the communications overhead. In this configuration, special care must be taken to maintain consistency between the client caches, as some disk blocks may be in use by more than one client. For this reason, most current distributed file systems do not provide a cache at the client machine. Those systems that do place restrictions on the types of file blocks that may be shared, or require extra communication to confirm that...

The number of users connected to the Internet has been growing at an exponential rate, resulting in similar increases in network traffic and Internet server load. Advances in microprocessors and network technologies have kept up with growth so far, but we are reaching the limits of hardware solutions. In order for the Internet's growth to continue, we must efficiently distribute server load and reduce the network traffic generated by its various services. Traditional wide-area caching schemes are client initiated. Decisions on where and when to cache information are made without the benefit of the server's global knowledge of the situation. We introduce a technique---push- caching---that is server initiated; it leaves caching decisions to the server. The server uses its knowledge of network topology, geography, and access patterns to minimize network traffic and server load. The World Wide Web is an example of a large-scale distributed information system that will benefit from this ge...

A practical problem faced by users of metacomputers and computational grids is: If my computation can move from one system to another, how can I ensure that my data will still be available to my computation? Depending on the level of software, technical, and administrative support available, a data grid or a distributed file system would be reasonable solutions. However, it is not always possible (or practical) to have a diverse group of systems administrators agree to adopt a common infrastructure to support remote data access. Yet, having transparent access to any remote data is an important, practical capability. We have developed the Trellis File System (Trellis FS) to allow programs to access data files on any file system and on any host on a network that can be named by a Secure Copy Locator (SCL) or a Uniform Resource Locator (URL). Without requiring any new protocols or infrastructure, Trellis can be used on practically any POSIX-based system on the Internet. Read access, write access, sparse access, local caching of data, prefetching, and authentication are supported. Trellis is implemented as a user-level C library, which mimics the standard stream I/O functions, and is highly portable. Trellis is not a replacement for traditional file systems or data grids; it provides new capabilities by overlaying on top of other file systems, including grid-based file systems. And, by building upon an alreadyexisting infrastructure (i.e., Secure Shell and Secure Copy), Trellis can be used in situations where a suitable data grid or distributed file system does not yet exist.

This paper presents an in-depth examination of the 4.2 Berkeley Software Distribution, Virtual VAX-11 Version (4.2BSD), which is a version of the UNIX’ ” Time-Sharing System. There are notes throughout on 4.3BSD, the forthcoming system from the University of California at Berkeley. We trace the historical development of the UNIX